Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Morristown Tennessee
315 PM EST Wednesday Dec 4 2013
Short term (tonight and thursday)...upper ridge over the area
shifts east tonight as short wave moves northeast through the Tennessee
Valley on Thursday. Cold front will move southeast through middle Tennessee
on Thursday. Warm air advection continues with southwesterly low
level flow. Temperatures well above normal in prefrontal airmass.
Dry middle levels moisten up on Thursday. Expect extensive cloud cover
through the period. Forecast problem is precipitation coverage.
Undercut blended MOS pop guidance by half for Thursday due to lack
of good trigger. Best chance appear to be across SW NC and the
plateau where low level convergence and upslope flow may aid
convective initiation. Thunderstorms become possible by Thursday
afternoon. Storm motion will be to the NE near 45 miles per hour. Deeper
convection should stay west of the area until late in the period.
Long term /Thursday night through Wednesday/...
unsettled weather will dominate the end of the week and beginning of
the new week as a strong upper-level storm system will impact the
region...bringing several rounds of precipitation and the potential
for some localized flooding. Models are in fairly good agreement of
showing a broad area of showers beginning to move into the region
along/ahead of a cold front moving in from the west. With deep
moisture available...widespread showers are expected late Thursday
night into Friday...before things begin taper off late Friday night
into Saturday. The concentration of the heaviest precipitation will
likely be to the north and west of the region...but a widespread
solid 1 to 2 inches...with locally higher amounts certainly seems
possible through Friday evening. With a boundary draped across the
region on Friday and some modest instability...some isolated strong
thunderstorms may also be possible during the day on Friday. Late
Friday night...some colder air working its way into the region may
also help to change over some wining precipitation over the northern
plateau to sleet. However...did not think that temperatures will
cool enough before the precipitation exits to make a mention of this
at this time.
After a brief break in the precipitation during the day Saturday...
the aforementioned boundary will lift back up to the north as a warm
front...and bring in some deep Gulf moisture from the south. This
will trigger off another round of locally heavy showers Saturday
night through Monday as deep upper-trough swings through the area.
The prolonged rainfall across the region may bring an additional 1
to 3 inches and cause a threat for flooding due to the already
saturated ground and the higher creeks/streams. A strong push of
colder air will then move in Monday night...changing over the
lingering showers on the backside of this system to snow showers as
the system winds down. Thereafter...dry and cold air will linger
across the region through the end of the period.
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 61 71 55 59 41 / 40 60 100 100 100
Knoxville McGhee Tyson Airport, Tennessee 55 72 54 61 38 / 10 40 80 100 100
Oak Ridge, Tennessee 57 71 52 55 38 / 30 50 90 100 100
Tri Cities Airport, Tennessee 51 70 53 62 37 / 10 30 70 90 100